Effects of the transported fluid composition and the pipeline route profile

Abstract

The modes of the transport of gas with low condensate content in an extentional subsea pipeline with a hilly terrain profile of the route are studied. Flow assurance in a pipeline is provided if the gas flow rate exceeds a certain threshold value called the turndown rate. It is shown that for a pipeline with a complex route profile, the transport of a two-phase hydrocarbon fluid (gas and condensate) is preferable to provide the flow assurance, since the presence of even a small amount of the water and hydrate inhibitor in the fluid leads to significant increase of the turndown rate. It is found that to expand the range of the safe pipeline operation, the use of methanol as a hydrate inhibitor is preferable over glycols. The performed hydraulic calculations show that the alignment of the pipeline route under construction may result in a decrease in the turndown rate for the transport of two-phase fluid and multiphase fluid containing a water solution of methanol. Keywords: subsea pipeline; natural gas; gas condensate; hydrate inhibitor; multiphase fluid; liquid holdup; turndown rate.